The present invention relates to a device for reducing a shift shock which is likely to occur when gear shifting is made by an automatic transmission of a car.
It has been a known practice to reduce a shift shock during an upshift of a car by decreasing an engine torque during shifting through the control of an ignition timing or a quantity of fuel injection for purpose of diminishing a difference in an inertia energy caused by a difference of engine speed between before and after shifting as stated in the specification of Japanese Patent Application No. 4-63138 pertaining to an application of the present patent applicant.
However, in gear shifting occurring during acceleration with the depth of depression of an accelerator pedal unchanged, that is, in a so-called automatic upshift, a gear ratio (engine speed/output shaft speed) after the shift becomes low; therefore a torque produced in the drive shaft varies step by step if the engine speed remains unchanging. To absorb this absolute torque change after shifting is made for the purpose of decreasing a shock at the time of shifting in order to insure smooth speed change, it is imperative to reduce the engine torque substantially during a short period of time. However, in such a construction that the engine torque is transmitted to the driving shaft side through a torque converter as in an automatic transmission, the engine torque can not be transmitted to the driving shaft side if the engine speed is not kept at some level. Here, the engine speed after upshifting lowers according to a gear ratio; therefore when a shock during shifting is lessened by decreasing the engine torque, there exists such a problem that if the engine torque is decreased excessively, the rate of decrease of the engine speed is accelerated to result in an engine speed drop after the completion of the shift, and in a driving torque drop after shifting and a lowered effect of shock reduction.
The present invention has been accomplished in an attempt to solve the aforementioned problem and has as its object the provision of a device and method for controlling an automatic transmission which is capable of eliminating a torque difference between before and after shifting, suppressing inertia variation during a shift, and further insuring driving safety without deteriorating operation performance even in the event of a sensor trouble.
To accomplish the aforementioned object, the control device pertaining to the present invention basically has a control means for controlling an engine torque and a transmission control means for controlling an automatic transmission; the control device comprising a means for nearly equivalently setting a driving torque immediately before starting a shift and a driving torque immediately after completion of the shift, and a means for suppressing a torque variation during gear shifting.
As a more concrete example, the control device has the control means for controlling the engine torque, the transmission control means for controlling the automatic transmission, and a means for reducing the engine torque during gear shifting, for the purpose of lessening a shift shock; the control device comprising a means for increasing the engine torque during a specific period before the completion of shifting than a common engine torque, and further for resetting the engine torque after a specific period after the completion of shifting to a common output.
Furthermore, the control device has the control means for controlling the engine torque, the transmission control means for controlling the automatic transmission, and the means for decreasing the engine torque during shifting, thereby lessening a shift shock; the control device comprising the means for nearly equivalently setting the driving torque immediately before the starting of shifting and the driving torque immediately after the completion of shifting, and a means for increasing the engine torque from a specific period before the completion of shifting than the common engine torque, and for resetting the engine torque after a specific period after the completion of shifting to a common output.
Furthermore, as a control means for controlling the engine torque, for example an electronic throttle valve or a large-capacity idle speed control valve and so forth may be used.
The engine torque at which the driving torques before and after shifting will become nearly equal is estimated from the gear ratio before and after shifting and characteristics of the torque converter, giving the engine the quantity of intake air occurring at this engine torque. During shifting, the quantity of intake air is decreased in accordance with a shift command signal and turbine rotation on the output side of the torque converter, thereby reducing the engine torque for the purpose of suppressing a driving torque variation by an inertia change. Furthermore, during the specific period before the completion of shifting, the amount of intake air is increased more than during a period of normal operation, thus lowering the rate of decrease in the engine speed in order to increase the engine torque. At the same time, the amount of intake air is reset to that during normal operation after the specific period after the completion of shifting, to prevent the drop of the engine speed after shifting, thereby restraining the drop of the torque converter output immediately before the shifting and realizing smooth shifting.